The Reason We Cannot See Earth’s Curvature When Standing on a Beach

We can’t directly observe and subjectively perceive the curvature of the Earth from a position close to the surface. And this matches the expectations in the spherical Earth model.

Flat-Earthers often take the fact we can see the curvature by standing on a beach as ‘evidence’ the curve doesn’t exist. They are, once again, wrong.

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Curvature Calculators and Atmospheric Refraction

Atmospheric refraction causes a distant object to appear higher than its actual position. As a result, the object can be physically behind Earth’s curvature but is still visible because the light coming from it is refracted by the atmosphere.

There are many curvature calculators and simulation tools that don’t account for refraction. They would give us the correct results indicating the object’s physical positions but fail to show us the correct apparent position of the object when visually observed.

Flat-Earthers are often too happy with the calculator showing them the results they want to see and fail to see the reason for the discrepancy.

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Water Level Demonstrates The Dip of the Horizon and Proves Earth’s Curvature

As the Earth is spherical, the horizon is below the eye-level (or the astronomical horizon). The angle between the eye-level and the horizon is the dip of the horizon. The angle becomes larger as we go higher.

Flat-Earthers often claim that “the horizon always rises to eye-level”, and thus ‘proving’ the flat Earth claim. Despite their insistence to use a water level to ‘prove’ water is flat, the same device can be used to demonstrate the dip of the horizon, proving the water surface has curvature, and consistent with the spherical Earth model.

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Perspective Compression: Determining If a Curvature Exists

Soundly’s pictures and videos of Lake Pontchartrain power lines and causeway stirred up the flat-Earthers’ nests. They clearly show the curvature of the Earth, where it is usually hard to discern. For the rest of us, those pictures are just the consequence of the fact that the Earth is a globe.

Flat-Earthers can’t take this, and they invented various excuses to attack the credibility of these pictures and videos. Some of them look for specific vantage point where it is impossible or very hard to discern the curvature.  They would conclude if the curve is not seen from these vantage points, then it should not be visible from Soundly’s viewpoints.

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Curvature of the Horizon in High-Altitude Balloon Footage

High-altitude balloon footage is often abused by flat-Earthers to show us that the Earth is flat when seen from a high altitude.

We analyzed more than two dozens of footage taken from high-altitude balloons on YouTube, and we can easily conclude the curvature is there and usually easy to spot, including in the cases where flat-Earthers use the video as ‘proof’ of a flat Earth.

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The Eratosthenes Experiment: Proving the Earth is Spherical

In 205 BC, Eratosthenes successfully determined the circumference of the Earth by measuring the length of the shadow cast by a rod. He did the measurement in Alexandria and timed it to coincidence when the Sun is directly overhead Syene.

2222 years after that, some flat-Earthers tried to refute the Eratosthenes experiment. They say the experiment can be applied to the flat-Earth model.

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The Curvature of the Water Surface

Flat-Earthers mention the curvature of water a lot. According to them, the curve of the water can never be observed, and thus, the Earth is flat.

The problem with such an argument is that they usually conclude that from a very small amount of water. Water in a glass or a bucket will practically look flat. Not because there is no curvature due to Earth’s gravity, but because the water is in such small amount so that the curvature is minuscule and impossible to observe, let alone with the naked eye.

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Atmospheric Refraction

Light waves are not always moving in a straight line. When it passes through a medium of a different refractive index, the waves will deviate. The phenomenon is called refraction and described according to Snell’s Law.

Earth’s atmosphere has variation in air density that depends on the altitude. As the refractive index changes with the density of the medium, light waves passing through Earth’s atmosphere also experience refraction.

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Zooming In On Distant Ships Does Not Disprove Earth’s Curvature

If we can’t see a distant ship, then it is because of one of these reasons:

  • Our eyes have limited angular resolution and are unable to resolve the ship at that distance.
  • The atmospheric condition is limiting our visibility.
  • The curvature of the Earth obscures the ship.

Flat-Earthers are keen to demonstrate that a previously invisible ship at a distance can be made visible by zooming in. They take this fact as ‘proof’ that the curvature of the Earth doesn’t exist. They are wrong. The curvature of the Earth is not the only reason a distant object is not visible.

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Perspective: Not the Reason a Sunset Occurs

One of the major holes in the flat-Earth model is the apparent motion of the Sun. The sun rises and sets once a day. But if the Earth is flat, then sunrises and sunsets should never happen, and the Sun would be visible all the time, from anywhere on Earth. In order to plug the hole and  ‘explain’ this problem, they invented an ad-hoc hypothesis that the Sun sets because of perspective.

The pretext is that an object appears closer to the horizon as it is moving away from the observer. They extrapolated this fact and wrongly assume that if it keeps going, then eventually it will appear to go down crossing the horizon line and is no longer visible.

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Difference in Entrance Pupil Diameter: The Real Reason Why An Obscured Object Appears When Zoomed In

Ever seen a video where a flat-Earther tries to demonstrate that a distant object that appears to be behind an obstacle can be brought back into view simply by zooming in? He would then conclude the same thing would happen when zooming in to a distant ship, and the reason a distant ship is not visible is not the curvature of the Earth.

Well, no. The real reason why the object in that experiment can be seen after zooming in is that the obstacle is close, and there’s difference in the camera’s entrance pupil size when the zoom changes. For a camera that has very long zoom range —like the Nikon P900—, the difference can be very dramatic.

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Lake Pontchartrain Power Transmission Lines: Evidence of Earth’s Curvature

Lake Pontchartrain is a lake in Louisiana, United States. There are power transmission lines about 24.27 km (15 mi) across this lake. They are practically straight, and each tower is uniform and has the same height, making these towers ideal for observing the curvature of the Earth.

They were first popularized by Soundly who presented evidence of Earth’s curvature using a series of photos and videos of the power lines in June 2017. As of now, the towers and other objects on the lake are probably the most popular Earth curvature tourism spot in the world.

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